The present invention relates to a color cathoderay tube apparatus such as a TV Braun tube or a monitor Braun tube, and more particularly to a color cathoderay tube apparatus in which no degradation occurs in focusing or distortion characteristics even where an electron beam trajectory correction means with a high degree of magnetic field distribution displacement is provided in realizing a flat screen by incorporation of a press-formed shadow mask.
In general, a color cathode-ray tube apparatus has a vacuum envelope comprising a panel with a substantially rectangular display section, a funnel formed to be continuous with the panel, and a cylindrical neck formed to be continuous with a small-diameter end portion of the funnel. A deflection yoke is mounted on a region extending from a funnel-side portion of the neck to a small-diameter portion of the funnel. An inner face of the panel is provided with a phosphor screen having dot-like or striped three-color phosphor layers which emit blue, green and red. A shadow mask is disposed to be opposed to the phosphor screen, at a distance from the phosphor screen. That surface of the shadow mask, which is opposed to the phosphor screen, has a great number of electron beam passage holes arranged with a predetermined pitch. The shadow mask has a so-called color selection function for guiding electron beams to the associated phosphor layers of the phosphor screen. The neck includes an electron gun apparatus for emitting three electron beams. The electron beams emitted from the electron gun apparatus are deflected horizontally and vertically by horizontal and vertical deflection magnetic fields produced by the deflection yoke, and the electron beams are directed to the phosphor screen through the shadow mask. The electron beams horizontally and vertically scan the phosphor screen and thus this screen displays a color image.
This kind of modern color cathode-ray tube apparatus is, in general, of an in-line type wherein three in-line electron beams comprising a center beam and a pair of side beams, which travel in the same plane, are emitted from the electron gun apparatus. In addition, most of practically used color cathode-ray tube apparatuses are of a self-convergence type wherein the horizontal deflection magnetic field produced by the deflection yoke has a pincushion shape and the vertical deflection magnetic field has a barrel shape, and the three in-line electron beams are deflected by the horizontal and vertical deflection magnetic fields, whereby the three electron beams can be converged over the entire screen without using a special convergence correction means.
Recently, there is a strong demand for flatness of the screen in this type of color cathode-ray tube apparatus. If the panel is flattened in order to realize the flatness of the screen, it is necessary to flatten the shadow mask, too. As a result, the following problem will arise.
In general, in the color cathode-ray tube apparatus, the three electron beams are converged at the center of the phosphor screen, mainly by a purity convergence magnet attached to the neck-side portion of the deflection yoke. The three electron beams pass through the electron beam passage holes in the shadow mask at predetermined angles, respectively, and land on the associated phosphor layers. In order to obtain a proper landing tolerance for the phosphor layers, it is required to properly set the distance between the inner face of the panel and the shadow mask.
Assume that, as shown in FIG. 1, a distance in a tube axis direction between a purity convergence magnet 1 and a shadow mask 2 is L (the distance L at the center of the phosphor screen is Lo), a distance in the tube axis direction between the shadow mask 2 and the inner face of a panel 3 is q (the distance q at the center of the phosphor screen is qO), a distance between a center beam 4G and each of paired side beams 4R, 4B in a direction of arrangement of the three electron beams is Sg (the distance Sg at the position of the purity convergence magnet is Sg0), a distance between the center beam 4G and the side beam 4B, 4R is "sgr", and a pitch of the landing position of the center beam 4G on the inner face of the panel 3 in the direction of arrangement of three electron beams is Ph (the pitch Ph at the center of the phosphor screen is Ph0). Since
q=Lxc3x97"sgr"/Sg
"sgr"=Ph/3
the following equation (1) is established:
q=Lxc3x97Ph/(3xc3x97g)xe2x80x83xe2x80x83(1)
Normally, the distance L and distance Sg are substantially constant over the entire area of the phosphor screen, and the pitch Ph, too, is basically constant. Accordingly, if the panel is flattened, it is necessary to flatten the shadow mask, too.
However, the shadow mask, in general, is manufactured by forming a flat, thin-plate-like shadow mask material, in which electron beam passage holes have been formed by photoetching, so as to have a predetermined curved surface. Using a forming apparatus as shown in FIG. 2, the shadow mask is formed to have a predetermined shape. Specifically, in the forming apparatus shown in FIG. 2, a non-hole portion 7 surrounding a region 6 with electron beam passage holes is clamped and fixed between a die 8 and a blank holder 9. The region 6 with electron beam passage holes is extended and formed in a predetermined shape by a punch 10 and a knockout 11. If the shadow mask is flattened and the amount of extension is reduced, plastic deformation cannot adequately be effected. The predetermined curved surface cannot be obtained due to degradation in workability. In addition, the strength of the formed shadow mask deteriorates and the shadow mask tends to be easily deformed.
FIGS. 3 and 4 show techniques for solving the above problems. In the techniques, trajectory correction means 14 and 15 for correcting the trajectories of the side beams 4R and 4B are provided between a cathode K of the electron gun apparatus, which emits three in-line electron beams 4R, 4G and 4B, and a phosphor screen 13. The trajectory correction means 14 and 15 exert force to the pair of side beams 4R and 4B, thereby to correct and turn the trajectories of the side beams 14 and 15 toward the center beam 4G. This force is made different between a central area and a peripheral area of the phosphor screen 13. More specifically, this force is varied in the following manner. That is, an imaginary distance Sg between the center beam 4G and the side beam 4R, 4B in the direction of arrangement of the three electron beams at the central area and peripheral area of the phosphor screen 13 is determined such that the distance Sg toward the peripheral portion of the phosphor screen 13 may be smaller than the distance Sg toward the center of the phosphor screen 13.
In the structure shown in FIG. 3, forces FrO and FfO produced by the two trajectory correction means 14 and 15 are set at zero at the center of the phosphor screen 13. In the peripheral region of the phosphor screen 13, the side beam 4B, 4R is over-converged by the force Fr1 produced by the neck-side trajectory correction means 14 and the side beam 4B, 4R is under-converged by the force Ff1 produced by the phosphor-screen-side trajectory correction means 15. Thereby, the imaginary distance Sg at the cathode K decreases from a distance Sgc0 to a distance Sgc1 from the center toward the periphery of the phosphor screen 13. Thus, the distance q in the tube axis direction between the inner face of the panel 3 and the shadow mask 2 at the peripheral region of the phosphor screen 13 is increased by a degree given below, relative to a distance q0 in the tube axis direction between the inner face of the panel 3 and the shadow mask 2 at the central region of the phosphor screen 13:
xcex94q=qxe2x88x92q0
Assume, in this case, that a distance in the tube axis direction between the phosphor screen-side trajectory correction means 15 and the phosphor screen 13 is Lf, a distance in the tube axis direction between the two trajectory correction means 14 and 15 is xcex94L, a distance Sg at the neck-side trajectory correction means 14 is Sgr0, and an over-convergence amount of the neck-side trajectory correction means 14 is CV1. The following equation (2) is established:
xcex94q=q0xc3x97xcex94Lxc3x97CV1/(2xc3x97Lfxc3x97Sgr0xe2x88x92xcex94Lxc3x97CV1)xe2x80x83xe2x80x83(2)
In the structure shown in FIG. 4, forces Fr1 and Ff1 produced by the two trajectory correction means 14 and 15 are set at zero at the peripheral region of the phosphor screen 13. At the central of the phosphor screen 13, the side beam 4B, 4R is under-converged by the force Ff0 produced by the neck-side trajectory correction means 14 and the side beam 4B, 4R is over-converged by the force Ff0 produced by the phosphor screen-side trajectory correction means 15. Thereby, the imaginary distance Sg at the cathode K increases from a distance Sgc1 to a distance Sgc0 from the periphery toward the center of the phosphor screen 13. Thus, xcex94q can be increased.
However, if the trajectory correction means 14 and 15 for over-/under-converging the paired side beams 4B and 4R in accordance with the position on the phosphor screen are provided, as described above, the degree of degradation in focusing characteristics or distortion characteristics increases as the amount of trajectory correction increases.
As has been mentioned above, in the color cathode-ray tube apparatus, if the panel is flattened, it is necessary to flatten the shadow mask, too, and the predetermined curved surface cannot be obtained due to degradation in workability. In addition, the strength of the formed shadow mask deteriorates and the shadow mask tends to be easily deformed.
To solve the problems, there is the technique wherein two trajectory correction means are provided between the cathode of the electron gun for emitting three in-line electron beams and the phosphor screen. The force produced by the trajectory correction means for correcting and turning the trajectories of the paired side beams toward the center beam is varied between the center portion and peripheral portion of the phosphor screen. The imaginary distance Sg between the center beam and the side beam in the direction of arrangement of the three electron beams at the central area and peripheral area of the phosphor screen is determined such that the distance Sg toward the peripheral area may be smaller than the distance Sg toward the center of the phosphor screen.
However, if the trajectory correction means for over-/under-converging the paired side beams in accordance with the position on the phosphor screen are provided, the problem arises in that the degree of degradation in focusing characteristics or distortion characteristics increases as the amount of trajectory correction increases.
The object of the present invention is to provide a color cathode-ray tube apparatus in which no degradation occurs in focusing or distortion characteristics even where electron beam trajectory correction means with a high degree of magnetic field distribution displacement is provided, for example, in realizing a flat screen by using a press-formed shadow mask.
According to the present invention, there is provided a color cathode-ray tube apparatus comprising:
a vacuum envelope composed of a substantially rectangular panel, a funnel formed to be continuous with the panel and having a small-diameter end portion, and a neck formed to be continuous with the small-diameter end portion of the funnel;
a phosphor screen having phosphor layers provided on an inner surface of the panel;
a shadow mask having a surface opposed to the phosphor screen at a distance from the phosphor screen, the surface having a great number of electron beam passage holes;
an electron gun apparatus provided within the neck and having a cathode and a plurality of electrodes for emitting three in-line electron beams consisting of a center beam and a pair of side beams traveling in the same plane;
a deflection yoke mounted on a region extending from a funnel-side portion of the neck to a small-diameter portion of the funnel, the deflection yoke deflecting the three electron beams in a first direction, which is a direction of arrangement of the three electron beams, and in a second direction perpendicular to the first direction; and
trajectory correction means for correcting trajectories of the side beams, the trajectory correction means including a plurality of trajectory correction coils disposed between the cathode of the electron gun apparatus and the phosphor screen and a current supply circuit for supplying to the trajectory correction coils a current synchronized with deflection of the first direction and/or the second direction, at least one of the trajectory correction means functioning to relatively over-converge or / under-converge the pair of side beams at a peripheral portion of the phosphor screen relative to a center of the phosphor screen, there is a position in a magnetic field produced in a region of passage of the three electron beams, where no force is exerted on the three electron beams in the first direction and/or the second direction, and a magnetic field being produced to separate this position from a plane including a tube axis, the first direction and/or the second direction.
According to the present invention, there is also provided a color cathode-ray tube apparatus comprising:
a vacuum envelope composed of a substantially rectangular panel, a funnel formed to be continuous with the panel and having a small-diameter end portion, and a neck formed to be continuous with the small diameter end portion of the funnel;
a phosphor screen provided on an inner surface of the panel;
a shadow mask having a surface opposed to the phosphor screen at a distance from the phosphor screen, the surface having a great number of electron beam passage holes;
an electron gun apparatus provided within the neck and having a cathode and a plurality of electrodes for emitting three in-line electron beams consisting of a center beam and a pair of side beams traveling in the same plane;
a deflection yoke mounted on a region extending from a funnel-side portion of the neck to a small-diameter portion of the funnel, the deflection yoke deflecting the three electron beams in a first direction, which is a direction of arrangement of the three electron beams, and in a second direction perpendicular to the first direction;
trajectory correction means for correcting trajectories of the side beams, the trajectory correction means including a plurality of trajectory correction coils disposed between the cathode of the electron gun apparatus and the phosphor screen and a current supply circuit for supplying to the trajectory correction coils a current synchronized with deflection of the first direction or the second direction, the trajectory correction means functioning to relatively over-converge or under-converge the side beams at a peripheral portion of the phosphor screen relative to a center of the phosphor screen; and
at least one auxiliary deflection means comprising a plurality of auxiliary deflection coils disposed between the cathode of the electron gun apparatus and the phosphor screen and a current supply circuit for supplying to the auxiliary deflection coils a current synchronized with deflection of the first direction and/or the second direction, the auxiliary deflection means effecting auxiliary deflection for the three electron beams at the peripheral portion of the phosphor screen in a direction opposite to the direction of deflection of the deflection yoke.
According to the present invention, there is also provided a color cathode-ray tube apparatus comprising:
a vacuum envelope composed of a substantially rectangular panel, a funnel formed to be continuous with the panel and having a small-diameter end portion, and a neck formed to be continuous with the small-diameter end portion of the funnel;
a phosphor screen provided on an inner surface of the panel;
a shadow mask having a surface opposed to the phosphor screen at a distance from the phosphor screen, the surface having a great number of electron beam passage holes;
an electron gun apparatus provided within the neck and having a cathode and a plurality of electrodes for emitting three in-line electron beams consisting of a center beam and a pair of side beams traveling in the same plane;
a deflection yoke mounted on a region extending from a funnel-side portion of the neck to a small-diameter portion of the funnel, the deflection yoke deflecting the three electron beams in a first direction, which is a direction of arrangement of the three electron beams, and in a second direction perpendicular to the first direction;
at least one trajectory correction means including a plurality of trajectory correction coils disposed between the cathode of the electron gun and the phosphor screen and a current supply circuit for supplying to the trajectory correction coils a current synchronized with deflection of at least the second direction, the trajectory correction means functioning to relatively over-converge or under-converge the pair of side beams at a peripheral portion of the phosphor screen relative to a center of the phosphor screen; and
auxiliary deflection means comprising a plurality of auxiliary deflection coils disposed between the cathode of the electron gun and the phosphor screen and a current supply circuit for supplying to the auxiliary deflection coils a current synchronized with deflection of the first direction and synchronized with deflection of the second direction and modulated, the auxiliary deflection means effecting auxiliary deflection for the three electron beams at the peripheral portion of the phosphor screen in the first direction.
According to the present invention, there is also provided a color cathode-ray tube apparatus comprising:
a vacuum envelope composed of a substantially rectangular panel, a funnel formed to be continuous with the panel and having a small-diameter end portion, and a neck formed to be continuous with the small-diameter end portion of the funnel;
a phosphor screen provided on an inner surface of the panel;
a shadow mask having a surface opposed to the phosphor screen at a distance from the phosphor screen, the surface having a great number of electron beam passage holes;
an electron gun apparatus provided within the neck and having a cathode and a plurality of electrodes for emitting three in-line electron beams consisting of a center beam and a pair of side beams traveling in the same plane;
a deflection yoke mounted on a region extending from a funnel-side portion of the neck to a small-diameter portion of the funnel, the deflection yoke deflecting the three electron beams in a first direction, which is a direction of arrangement of the three electron beams, and in a second direction perpendicular to the first direction;
at least one trajectory correction means including a plurality of trajectory correction coils disposed between the cathode of the electron gun and the phosphor screen and a current supply circuit for supplying to the trajectory correction coils a current synchronized with deflection of at least the first direction, the trajectory correction means functioning to relatively over-converge or under-converge the pair of side beams at a peripheral portion of the phosphor screen relative to a center of the phosphor screen; and
auxiliary deflection means comprising a plurality of auxiliary deflection coils disposed between the cathode of the electron gun and the phosphor screen and a current supply circuit for supplying to the auxiliary deflection coils a current synchronized with deflection of the second direction and synchronized with deflection of the first direction and modulated, the auxiliary deflection means effecting auxiliary deflection for the three electron beams at the peripheral portion of the phosphor screen in the second direction.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.